Pile driver drive cap

ABSTRACT

A water-cooled drive cap for use with pile driving machines which also includes a sensing construction actuatable either electrically or pneumatically to provide an indication of the force of the blow of the hammer of the pile driver and thereby prevent overdriving of the pile and to determine the static load bearing capacity of the pile.

United States Patent [19] Frederick [4 1 June 18, 1974 1 PILE DRIVER DRIVE CAP [76] Inventor: Leonard L. Frederick, 15 Crestview Ter., Whippany, NJ. 07981 [22] Filed: May 11, 1971 [21] Appl. No.: 142,174

[52] US. Cl 73/84, 73/12, 73/141 A, 173/139 [51] Int. Cl. G0ln 33/24 [58] Field of Search 73/84, 11, 141 A, 12; 173/80, 139

[56] References Cited UNITED STATES PATENTS 3,226,974 1/1966 Bresk et a1 73/12 3,242,997 3/1966 Tokola 173/139 X 3,483,741 12/1969 Paelian et a1. 73/141 A 3,498,388 3/1970 Jovis 73/84 X 3,535,919 10/1970 Budlong et a1 73/509 X FOREIGN PATENTS OR APPLICATIONS 226,917 6/1969 U.S.S.R 73/84 286,480 3/1928 Great Britain 713/84 Primary Examiner-Jerry W. Myracle Attorney, Agent, or FirmEdwin E. Greigg; Everett G.

Clements 5 7 ABSTRACT A water-cooled drive cap for use with pile driving machines which also includes a sensing construction actuatable either electrically or pneumatically to provide an indication of the force of the lblow of the hammer of the pile driver and thereby prevent overdriving of the pile and to determine the static load bearing capacity of the pile.

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v A/EL H08 3 I 519; NER- NIRWEV O .8 I q INVENTOR LEONARD L. FREDERICK ATTORNEY PILE DRIVER DRIVE CAP This invention relates to drive cap construction used in connection with pile driving and more specifically to a new type of water cooled elastomer cushioned drive cap with means for sensing the force of each blow as the pile is driven to prevent damage to the pile from overdriving and to determine the static load bearing capacity of the pile.

BACKGROUND OF THE INVENTION Drive caps for pile drivers fit over the head of the pile and transmit the hammer blows evenly to the pile while at the same time maintaining the head of the pile in alignment with the hammer by guiding the head parallel to the leads frame and retaining the pile in a straight predetermined path. It is desirable that the drive cap be adaptable to many or all types and sizes of piles such as timber or wood pile, concrete pile, H-beams, pipe pile, fluted pile and the like, each being held properly centered on the driving axis. Further, as the pile is driven, the operator must be careful to control the force of the blows so as not to exceed the elastic limit of the pile material (overdriving) in order to minimize costly tip damage.

The continuous pounding of the hammer upon the drive cap produces heat from hysteresis in the cushioning material used to cushion the blows, which heretofore have been made of wood, thus causing charting and burning and consequent destruction and requiring frequent replacement at considerable cost, as well as delay in operations. I

With present equipment after a pile is driven, its maximumstatic bearing load must then be determined by a dead load bearing test which is costly in both time and material. The drive cap described in the following specification therefore provides new and novel means for providing greater endurance for the cushioning material by reducing the heating effect of the elastomer pad, as well as establishing an accurate methodof measuring the dynamic force of each blow thereon and also furnishing means for determining the equivalent static Accordingly, it is the principal object of the invention to provide a transducer that will measure the maximum threshold force from the hammer that can be applied to the pile without causing permanent penetration of the pile or set into the ground. Thus, the maximum bearing capacity of the pile can be determined immediately, and thus eliminate the costly dead load bearing test. Moreover, costly overdriving of the pile may also be minimized and pile tip damage reduced.

It is also an object of the invention to provide a drive cap for aligning the head of the pile with the hammer which embodies a liquid cooled elastomer cushion so that pile head damage is reduced to a very minimum while driving the pile. Internal heat generated by the hysteresis of the elastomer cushion due to the continuous pounding is dissipated and will therefore prevent damage to the pad from burning or charring as well as affording greater endurance thereof and providing a more efficient cushioning effect.

Another object of this invention is to provide a drive cap with means for sensing the force of each hammer blow and displaying the force in the cab and to the operator in order that he may. control each impact force whereby they will not exceed the elastic limit of the pile material, thereby preventing permanent damage to the pile.

Still another object of this invention is to provide a means whereby the operator in the cab of the pile driver may determine the maximum bearing load that the pile will support without the need for a costly dead load bearing test.

Yet another object of this invention is to provide a drive cap which will fit both American style box leads with side rails and European style leads with rails or ways which are customarily provided to the rear of the hammer and cap. A further object is to provide a cap which will fit a large concrete pile and through the use of adapters can be made to accommodate other types of piles, such as wood, steel, H-beams and steel pipe. The adapter may be so constructed that it may be easily replaced and fastened without disassembly of the cap or its cushion.

Still further objects are to provide a cap with the front and one side shorter, and the back and other side beveled inwardly, so the pile head can be fed or guided into the bottom cavity of the cap easily and to further provide a circular upper cavity with a shallow bottom radius for easy alignment of the pile driver anvil.

Still another object is to provide a cap which includes two cushions, one of which receives the impact of the hammer and the other the impact of the pile, with each cushion being water cooled.

These and other objects of the invention will become more apparent from a reading of the following specification taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a top plan view of the drive head with the chambers therewithin for circulation of the coolant being depicted in phantom lines;

FIG. 2 is a front elevational view with portions of the cap cutaway to show the configuration of the head as well as the position of the elastomeric cushion;

FIG. 3 is a view looking into the right side of the drawing shown in FIG. 2 with portions cutaway to show the water circulation between the chamber and the elastomeric cushion;

FIG. 4 is a top plan view of the liquid cooled elastomer transducer cushion;

FIG. 5 is an elevational view, partially in section, of the transducer cushion;

FIG. 6 is a schematic of the electrical circuitry required to read the force of the hammer blows;

FIG. 7 is a plan view with portions cut away of a further embodiment of the water-cooled drive cap looking down into the water-cooled chamber;

FIG. 8 is a cross-sectional view on line 8-8 of FIG.

FIG. 9 is a top plan view of a further embodiment of the elastomeric cushion; and

FIG. 10 shows the cushion partly in elevation and partly in cross section on line AA of FIG. 9.

DESCRIPTION OF THE EMBODIMENTS Turning now to FIG. 1, there is shown a top plan view of the drive cap 10 which comprises an integral cast or forged body portion of substantially rectangular shape having guide lugs 11-11 offstanding diametrically from the opposite sides thereof, these lugs being adapted to be complemental to American leads. The planar guide lugs 12-ll2, which offstand laterally from the rear wall, are arranged to be complemental to European leads. The upper portion of the cap is provided with a circular cavity 13 and includes a concave face 14 which is more clearly shown in FIG. 2, and is adapted to align and hold the hammer anvil on the driving axis.

Referring at this time to FIG. 3 and more particularly to cross-sectional area to the right of this view, there is shown at 15 a portion of a water or other suitable heat transmitting liquid reservoir which constitutes a head member with the fill means therefor being shown at 16.

In this view are also clearly shown means defining perforations at 17 and 18 which are provided in the inner wall of the reservoir, as at 19, and which will serve to provide for circulation of the coolant through the perforations 20 in the segmentally arranged wall portions 22 forming chambers 22a. This is best shown in FIG. 1.

As is also well shown in FIG. 3, there is illustrated at 23 an upper planar wall, the inner portion of which forms the top of the aforesaid liquid filled chamber, on the concave exterior portion of which the pile driver is adapted to be received and lying in a plane parallel therewith, and therebeneath is the perforate bottom wall 24 of the chamber with the perforations therein being indicated at 25. With further reference to this view there is also shown at 26 an adapter which is only representative of one type of adapter that is available, the perimeter thereof conforming to the interior of the head with its upper surface being flat for a purpose that will now be described, and its lower surface being formed complementally to receive the upper planar surface of the particular type of pile to be driven, this pile being shown in phantom lines at P. The perimeter of the adapter is provided with means defining openings in the wall thereof, as at 34, and these are aligned with perforations 35 in the housing 10 so that suitable cable means may be availed of to secure the adapter to the head.

The elastomer cushion, which constitutes the primary inventive concept of this invention, is well shown in the top plan view in FIG. 4; however, it is believed that its cooperation with the elements comprising the drive cap will be best understood by a further study of FIG. 3. In this view it will be observed that the elastomer cushion 27 is provided with a channel 28 which lies directly beneath the perforations of the wall 24.

It is believed that from a study of this view it will be appreciated that as a hammer blow is applied, the elastomeric cushion 27 is squeezed together causing the liquid which is in groove 28 to rush up into the chamber thereabove and then flow back again to the cushion as the hammer is lifted, thus giving a rapid circulation or agitation of the liquid within the reservoir, thus transferring the heat due to hysteresis in the cushion to the outer walls of the head where it is lost by convection and radiation. In the present drawings though the only cooling is accomplished within the head 10, it will be obvious to those skilled in the art that for heavy loadings where heat generation is high, fins may be added to the exterior of the head to increase the cooling area and in addition the liquid may be circulated through the head from a heat exchanger.

By now referring to the view of FIG. 4, it will be noted that the channel 28 follows a more or less tortuous path which includes an inner end that terminates substantially in the center of the cushion at 29 while the outer end of the channel terminates adjacent to one edge of the pad at 30. The entire outer side wall area of the cushion is provided at the upper edge portion with an outwardly extending lip 31 which, it will be apparent from an examination of FIG. 3, forms a liquid seal to prevent the coolant medium from escaping from the channel area and leaking about the inner wall 19 of the reservoir. This is best understood by reverting to FIG. 3, the cross-sectional view showing the elastomer cushion in position between the wall 24 and the adapter 26.

With further reference to FIG. 3, it will be noted that there is cast into the elastomer cushion 27, a capacitance transducer that can serve, together with a current amplifier and an oscillograph, to measure the impact blow of the hammer on the head of the pile, as will now be explained in more detail.

Turning now to FIG. 6, there are shown schematically therein plates 34a and 35a of a capacitor 40 which represents the wires 34 and 35 which are encapsulated within the elastomeric cushion 27. In parallel with the capacitor 40, between points 41 and 42, there is a voltage source 43 in series with a high resistance 44 limiting the ability of the voltage source 43 to rapidly charge the capacitor. The leads from the two wires 34 and 35 are arranged as shown in FIG. 2 to extend out of one side of the cushion and pass through insulated bushings 28a which are provided in the head 10.

Initially, the wires 34 and 35 in the elastomeric cushion 27 schematically indicated as plates 34a and 35a in FIG. 6 are connected to the voltage source 43 through resistor 44 and current flows until the plates are charged and the potential across the plates equals that of the voltage source.

When the hammer strikes the cap, the elastomeric cushion 27 is squeezed together between the bottom surface of plate 24 and the adapter cap 26, thus causing the initial encapsulated point of separation between the wire mesh screen capacitor plates 34a and 35a to be reduced. The capacitor thereby attains an excess charge which starts to bleed off. When the elastomeric cushion 27 springs back to shape upon the hammer being lifted away from the surface 14, the separation of the plates 34a and 35a is suddently increased and the capacitor thereupon being lacking in its charge, attempts to draw current through resistor 44. Since the resistor 44 is large, it creates a voltage drop and instantaneously causes a voltage drop across the plates 34a and 35a, as well as points 41 and 42. This voltage is then applied to the terminals 48 and 49 of high persistance screen oscilloscope 53 through wires 45 and 46 and can be interpreted in terms of peak force since the squeezing of the elastomeric cushion 27 is proportional to the force of the hammer and therefore the plate separation is proportional to the force of the hammer. Depending upon the specific parameters of the plate size, separation and voltage for a particular method, an amplifier 47 may be required and this is shown in phantom ahead of the oscilloscope input terminals.

It will be recognized by those skilled in the art that there are many other known ways of detecting and displaying a change in capacitance, for example, through more sophisticated systems detecting frequency changes in the tank circuit of which the wires 34!- and 35 are a part.

By the interpretation of peak force, the operator can adjust the hammer blows so that the elastic limit of the pile material is not exceeded, thereby eliminating damage to the pile tip.

Secondly, the system can be used to determine the static bearing load on a pile after it is driven. By reducing the blow force of the hammer to an amount where the pile ceases to make any further penetration, the force level can be recorded which will be the maximum bearing capacity of the pile, thus eliminating the need of a separate dead load bearing test.

With reference at this time to FIG. 7, there are clearly shown in this view the guide lugs 75 and 76 for American and European style leads respectively, the purpose of which was explained earlier herein.

Also, illustrated in this cross-sectional view are a plurality of chambers 77, each of which is interconnected by means of perforations 78 and by means of which coolant from the surrounding compartments 79, 80 (best seen in FIG. 8) is arranged to circulate and there after traverse by way of perforations 81 in the spaced walls 82 and 83 and thereby be brought into communication with the opposed channelized areas 84 and 85, respectively, of the elastomeric cushions 86 and 87.

As described earlier in connection with the electrical transducer concept, as well shown in FIGS. 4 and 5, which constitutes the first embodiment of this invention, reference is made at this time to the pneumatic impact transducer illustrated in FIGS. 9 and 10.

As shown in the plan view of FIG. 9, the elastomeric cushion 87 includes a water coolant channel area 85 such as that described earlier relative to FIGS. 4 and 5, this being illustrated clearly in this view. In addition thereto, as illustrated in dotted outline in this figure, there is provided a circuitous path 88 into which air pressure is introduced.

In view of the detailed description of the first embodiment of this invention, which clearly sets out how the electrical transducer is arranged to function, it would appear sufficient to indicate that as the cushion 87 of this later embodiment is depressed by the impact force of the hammer against the cushion and thereinto the metallic drive cap, that the circuitous cavity is flattened sufficiently to cause the air contained therein to be expelled or discharged into a pressure gauge which is mounted in a clear view position in front of the hammer operator in the cab of the machine.

It will be understood from the earlier description of FIGS. 4 and 5 that here also as the hammer is lifted and lowered in this embodiment of the invention, the air which travels to and from the pressure gauge will provide a clear indication to the operator not only of the force of the hammer but also the static load bearing capacity of the pile being driven.

In the earlier embodiment of the drive head, the circular cavity 13 was shallow as is best shown in FIGS. 2 and 3. However, by reason of the fact that in the second embodiment the elastomeric cushion 86 is positioned in the cavity 90 in the head, the walls thereof must necessarily be higher to receive both the elastomeric cushion and the hammer.

The perimeter of the elastomeric cushion 87, which is positioned between the pile and the wall 83 of the head, is designed to be received snugly within the smooth surface area 91 of the drive cap and is arranged so that when the cushion is in its relaxed condition, water pressure can be emitted from the chambers 77 into the cushion without developing any leakage between theperimeter of the cushion 87 and the surface area 9i. Cushion 86 is similarly arranged with respect to its surrouding wall 9%.

The invention disclosed hereinb efore illustrates several commercial embodiments of this invention, but the structure may be modified or changed while still maintaining the true intent of the invention as hereinafter defined and claimed.

That which is claimed is:

l. The method of determining the static load bearing capacity of a pile comprising driving the pile into the ground by a series of blows, adjusting the force of the blows to the maximum threshold impact that can be applied to the pile without causing permanent penetration or set of the pile, sensing the force of the blows to produce said threshold impact and indicating said sensed force whereby the static load bearing capacity of said pile is determined.

2. The method of claim 1 comprising indicating said force in terms of the static load bearing capacity of the pile.

3. The method of claim 1, comprising transmitting said blows through a sensing means including an elasto meric cushion to the top of the pile to alter the relative vertical position of at least portions of said sensing means, and circulating liquid in a passage in said elastomeric cushion to cool said cushion.

4. The method of claim 3 comprising causing the liquid in said passage to surge back and forth between said passage and a reservoir in synchronism with said blows.

5. The method of claim 1 comprising laterally confining an elastomeric cushion containing means for sensing the force of said blows and transmitting said blows through said sensing means to the top of the pile to alter the relative vertical position of at least portions of said sensing means.

6. The method of claim 5 comprising circulating liquid in a passage in said elastomeric: cushion to cool said cushion. 7. A drive cap for receiving blows and transmitting them to the top of a pile comprising a body portion having a recess and an elastomeric cushion positioned in said recess, said cushion being positioned in the line of force transmission of said blows to the pile when said cap is positioned on top of a pile, means for sensing the force of said blows embedded in said cushion, said sensing means having vertically spaced portions which are adapted to change their relative position under the force of said blows and means for cooling said elastomeric cushion comprising a passage for cooling liquid positioned in the body of said cushion.

8. A drive cap as claimed in claim 7, wherein said body portion includes an enclosed space for containing a supply of said cooling liquid, a wall separates said enclosed space from the elastomeric cushion and a perforation in said wall connects said passage to said space for flow of said liquid.

9. A drive cap as claimed in claim 8, wherein said space is bounded by a second wall which is vertically spaced from said first mentioned wall and is substantially parallel thereto, each of said walls extending horizontally and being adapted to transmit the force of said blows to said pile, and partition walls connect said first and second walls to form a plurality of chambers between said first and second walls, perforations in said partitions providing for circulation of said cooling liquid between said chambers.

10. A drive cap as claimed in claim 9 wherein said passage in said cushion is of generally spiral form, a plurality of perforations connect said passage to said chambers and said vertically spaced portions of said sensing means are of generally spiral form and positioned adjacent said passage.

11. A drive cap as claimed in claim 10, wherein said sensing means is an electrical condenser.

12. A drive cap as claimed in claim 11, wherein the elastomeric cushion is confined against lateral expansion.

13. A drive cap as claimed in claim 7, wherein the elastomeric cushion is confined against lateral expansion.

14. A drive cap as claimed in claim 7, wherein said means for sensing includes a pneumatic impact transducer.

15. A pile driving apparatus having a hammer for driving a pile and including an elastomeric cushion adapted to transmit blows from said hammer to the top of said pile, means for cooling said elastomeric cushion comprising a passage for cooling liquid positioned in the body of said cushion, means for sensing the force of said blows embedded in the cushion, said sensing means having vertically spaced portions which are adapted to change their relative position under the force of said blows and said sensing means being connected to means for receiving a signal from said sensing means and indicating static load bearing capacity of said pile.

16. A pile driving apparatus as claimed in claim 15, wherein said elastomeric cushion is confined against lateral expansion.

17. A pile driving apparatus as claimed in claim 16, wherein said sensing means is an electrical condenser and is electrically connected to said means for indicating the static load bearing capacity of the pile, said indicating means comprising an electric circuit. 

1. The method of determining the static load bearing capacity of a pile comprising driving the pile into the ground by a series of blows, adjusting the force of the blows to the maximum threshold impact that can be applied to the pile without causing permanent penetration or set of the pile, sensing the force of the blows to produce said threshold impact and indicating said sensed force whereby the static load bearing capacity of said pile is determined.
 2. The method of claim 1 comprising indicating said force in terms of the static load bearing capacity of the pile.
 3. The method of claim 1, comprising transmitting said blows through a sensing means including an elastomeric cushion to the top of the pile to alter the relative vertical position of at least portions of said sensing means, and circulating liquid in a passage in said elastomeric cushion to cool said cushion.
 4. The method of claim 3 comprising causing the liquid in said passage to surge back and forth between said passage and a reservoir in synchronism with said blows.
 5. The method of claim 1 comprising laterally confining an elastomeric cushion containing means for sensing the force of said blows and transmitting said blows through said sensing means to the top of the pile to alter the relative vertical position of at least portions of said sensing means.
 6. The method of claim 5 comprising circulating liquid in a passage in said elastomeric cushion to cool said cushion.
 7. A drive cap for receiving blows and transmitting them to the top of a pile comprising a body portion having a recess and an elastomeric cushIon positioned in said recess, said cushion being positioned in the line of force transmission of said blows to the pile when said cap is positioned on top of a pile, means for sensing the force of said blows embedded in said cushion, said sensing means having vertically spaced portions which are adapted to change their relative position under the force of said blows and means for cooling said elastomeric cushion comprising a passage for cooling liquid positioned in the body of said cushion.
 8. A drive cap as claimed in claim 7, wherein said body portion includes an enclosed space for containing a supply of said cooling liquid, a wall separates said enclosed space from the elastomeric cushion and a perforation in said wall connects said passage to said space for flow of said liquid.
 9. A drive cap as claimed in claim 8, wherein said space is bounded by a second wall which is vertically spaced from said first mentioned wall and is substantially parallel thereto, each of said walls extending horizontally and being adapted to transmit the force of said blows to said pile, and partition walls connect said first and second walls to form a plurality of chambers between said first and second walls, perforations in said partitions providing for circulation of said cooling liquid between said chambers.
 10. A drive cap as claimed in claim 9 wherein said passage in said cushion is of generally spiral form, a plurality of perforations connect said passage to said chambers and said vertically spaced portions of said sensing means are of generally spiral form and positioned adjacent said passage.
 11. A drive cap as claimed in claim 10, wherein said sensing means is an electrical condenser.
 12. A drive cap as claimed in claim 11, wherein the elastomeric cushion is confined against lateral expansion.
 13. A drive cap as claimed in claim 7, wherein the elastomeric cushion is confined against lateral expansion.
 14. A drive cap as claimed in claim 7, wherein said means for sensing includes a pneumatic impact transducer.
 15. A pile driving apparatus having a hammer for driving a pile and including an elastomeric cushion adapted to transmit blows from said hammer to the top of said pile, means for cooling said elastomeric cushion comprising a passage for cooling liquid positioned in the body of said cushion, means for sensing the force of said blows embedded in the cushion, said sensing means having vertically spaced portions which are adapted to change their relative position under the force of said blows and said sensing means being connected to means for receiving a signal from said sensing means and indicating static load bearing capacity of said pile.
 16. A pile driving apparatus as claimed in claim 15, wherein said elastomeric cushion is confined against lateral expansion.
 17. A pile driving apparatus as claimed in claim 16, wherein said sensing means is an electrical condenser and is electrically connected to said means for indicating the static load bearing capacity of the pile, said indicating means comprising an electric circuit. 